1. Field
The following description relates to an apparatus and method for soft demapping that may calculate a log likelihood ratio (LLR) value with respect to a quadrature amplitude modulation (QAM) signal.
2. Description of Related Art
In an effort to enhance the performance of a broadcasting communication system, a signal space diversity (SSD) method of a rotated constellation form may be applied to digital video broadcasting-second generation terrestrial (DVB-T2).
When calculating a log likelihood ratio (LLR) value using a diversity gain of a received signal, quadrature amplitude modulation (QAM) performance may increase in a fading channel. However, because a constellation may rotate along an in-phase (I)-quadrature (Q) plane, it is difficult to secure the independency of an I channel and/or a Q channel. That is, by simply applying existing one-dimensional (1D) max-log LLR demapping, a diversity gain may be lost.
As another example, by applying two-dimensional (2D) LLR demapping simultaneously using a value of the in-phase (I) channel and a value of the quadrature (Q) channel to an M-QAM signal, an amount of calculations may increase by a few times or more in comparison to an existing amount of calculations.
Accordingly, there is a desire for an algorithm that may enhance the performance of the full search 2D LLR calculation with a smaller amount of calculations.